Cytokines play a key role in the pathogenesis of chronic Graft versus Host Disease (cGVHD) and various studies have shown abberant production of cytokines by immune cells from GVHD patients. Based on these findings and others showing that high TNF levels precede the development of GVHD, we evaluated inflammatory cytokine levels following BMT and during the development of cGVHD. In this study, patients undergoing bone marrow transplantation (BMT) who consequently developed chronic GVHD were analyzed as to their cytokine production during cGVHD and this was correlated with their clinical manifestations. A positive correlation was found between the severity as well as the number of major clinical complications and high levels of inflammatory cytokines (IL-1bTIL-6 and TNFaL) compared to control patients or to normal donors. Patients undergoing BMT who did not develop GVHD, did not produce high levels of IL-1 (bTIL-6 or TNF. High levels of cytokines may be used as a tool for assessing novel therapeutic modalities and response to GVHD treatment.